Structures of bacterial iron-containing proteins, several functional in bioconversion of solar energy, as being determined. Many of these proteins, available in pure form and bulk quantities, have been crystallized and the resultant preparations found adequate for tertiary structure determinations at high resolution, using a variety of procedures including x-ray crystallographic analysis, and a wide range of modern spectrochemical methodology (ORD, CD, NMR, e.g. EPR, IR, and MCD spectroscopy). These preparations include the variant bacterial cytochromes c (cytochrome c2, cytochrome c' and "HiPIP"), and cytochromes "F" of red and blue-green algae. Complete amino acid sequences for many of these proteins have been determinded. Others are now being analyzed in extension of these structure studies to provide a detailed molecular basis for a comparative biochemistry of iron-containing proteins.